Differential roles of copper-binding transcription factors and the subfamilies of the SWI/SNF complex in the transcriptional regulation of the skeletal muscle lineage [RNA-seq]

Copper (Cu)-binding transcription factors are emerging as important regulators of gene expression during skeletal muscle differentiation. Our group has shown that the classic Metal Transcription Factor 1, MTF1, works cooperatively with the myogenic factor MyoD to promote skeletal muscle differentiation and ensure viability of murine primary myoblasts. Preliminary evidence showed that MTF1 interacts with members of the mammalian SWItch/Sucrose Non-Fermentable (mSWI/SNF) family of ATP-dependent chromatin remodeling enzymes to promote differential gene expression in proliferating and differentiating myoblasts. mSWI/SNF complexes are assembled into three major subfamilies that are distinguished by the presence of mutually exclusive subunits: cBAF (canonical BRG1 or BRM-Associated Factor), PBAF (Polybromo containing BAF), or ncBAF (non-canonical BAF). The mechanisms by which each subfamily contributes to the establishment or function of specific cell lineages are poorly understood. We determined the contributions of the BAF, ncBAF, and PBAF complexes to myoblast proliferation, differentiation, and metal homeostasis via knock-down (KD) of a distinguishing subunit of each complex (Baf250A, Brd9, and Baf180, respectively). Biochemical, molecular and RNA-seq analyses showed that Baf250A KD reduced myoblast proliferation rate and differentiation. Brd9 KD resulted in a minor proliferation defect and a delay in myogenesis. KD of Baf180 and other PBAF-specific subunits did not impact proliferation or differentiation but affected the maintenance of metal homeostasis in myoblasts. The data support a model for differential roles and interactions between MTF1 and a novel category of Cu-binding transcription factors and the SWI/SNF enzymes in the development and homeostasis of the skeletal muscle lineage.